Shares of Ionis Pharmaceuticals (NASDAQ:IONS | IONS Price Prediction) are down 9% intraday, changing hands near $58.30 after opening the session at $64.27. The slide caps a brutal stretch for the RNA-targeted drug developer, with the stock now off over 25% over the past week.
Phase 3 Heart Trial Failure Drives the Selloff
The catalyst is a clinical setback. On July 9, 2026, Ionis and partner AstraZeneca disclosed that the Phase 3 CARDIO-TTRansform study of eplontersen in transthyretin-mediated amyloid cardiomyopathy (ATTR-CM) failed to meet its primary efficacy endpoint in the overall patient population. That is the same program flagged as a key value driver heading into the back half of 2026, and the reaction has been swift.
Peers Mostly Lower, but Rivals in ATTR-CM Stand to Benefit
The reaction across RNA and rare-disease biotech is uneven. Alnylam Pharmaceuticals (NASDAQ:ALNY), whose Amvuttra competes directly in ATTR-CM, is down 3.6% to $302. That is a notable move given that Benzinga flagged Amvuttra as one of the rivals standing to gain from the eplontersen miss, alongside BridgeBio’s Attruby. The initial read from the Street is that existing second-generation monotherapies now face less near-term competitive pressure.
Arrowhead Pharmaceuticals (NASDAQ:ARWR), another RNAi developer, is down 8.3% to $77, tracking the sector sympathy move despite the mostly unrelated business. Sarepta Therapeutics (NASDAQ:SRPT) is off 6.5% to $19. Ionis collaborator Biogen (NASDAQ:BIIB), which co-develops multiple antisense assets with Ionis, is bucking the group and trading up 0.5% to $200.
Ionis was priced for a lot going into this readout. The stock had roughly doubled over the past year until July 7th.
What to Watch Next
Two catalysts sit directly in front of investors. The full CARDIO-TTRansform dataset lands at ESC in August, which will help point to any subgroup opportunities. The zilganersen PDUFA for Alexander disease is set for September 22, 2026, followed by the bepirovirsen decision in chronic hepatitis B on October 26. Keep an eye on whether Ionis holds above the $40 52-week low as the dust settles.
Contact [email protected] for any questions or corrections.
Top Gaining Stocks
Top Losing Stocks